Have you ever come upon the realization, late in the afternoon, that you haven't had any water to drink all day? It seems like an obvious thing to do throughout the day, but in practice, it can actually be kind of hard to remember to drink water, and it's often especially challenging to sip the total, recommended eight glasses of H2O a day. But truth be told, since water is needed for basically every single function in your body, it's important to know how to recognize the subtle signs you're dehydrated, because the thing is, it can be hard to tell that lack of water, of all things, is the culprit behind your lethargy or your mood swings.

For what it's worth, dehydration is actually really common. Whether you're neglecting to replenish your body's fluids after a sweaty workout, or your go-to drink throughout a typical work day is a sugary soda, it's so easy to let hydration fall by the wayside in your everyday routine. As reported in The Daily Mail in 2015, a survey of300 general practitionersin the UKfound that about one in five patients were going to their doctors with health concerns that were ultimately traced back to mild dehydration. What's more, the news outlet said, only 4 percent of doctors in the survey said they believed their patients were actually aware of just how much water they should be drinking per day.

So go ahead and spread the word, OK? And, keep in mind, the amount of water you need may differ from the eight-glasses rule, depending on your size and individual health concerns. But if you notice any of these six signs, then you'll definitely know it's time to amp up your hydration.

1You're Groggy And Grumpy For No Apparent Reason

If you're feeling groggy AF all the time, even though you know you've been getting enough sleep, drinking some water might be the first step to getting your energy back up. To add to that, not having enough water can cause you to not only lack focus and feel fatigue, but it can make you grumpy, too.

2You Aren't Peeing Very Much

When it comes to dehydration, a good (and maybe a little obvious) rule of thumb is to remember that what's going into your body is eventually going to come out. So, if you aren't peeing a lot, then yes, that might definitely be a sign you should be drinking more H2O.

3You Have A Splitting Headache That Even Advil Can't Solve

Sure, maybe your head hurts from stress, but it could also be due to the fact that you keep forgetting to pour yourself some water throughout the day.

According to Medical News Today, your brain can actually contract, or shrink temporarily when you don't drink enough water, causing the brain to pull away from the skull — and yes, it's basically as painful as it sounds. But as long as you chug that H2O, you can avoid that discomfort at all costs.

4Your Skin Is Acting Up Out Of Nowhere

Your skin can actually react in a few different ways when you aren't drinking enough water. According to Dermalogica, there's a difference between dry skin and dehydrated skin: Dry skin is a characteristic of your unique skin makeup, whereas dehydrated skin is circumstantial — i.e. you're not getting enough H2O throughout the day.

If you aren't drinking enough water, then you might notice your skin is a bit flaky, or you might have little, irritated patches scattered around. However, Dermalogica explains, some people's skin can over-produce oil in response to dehydration, causing breakouts as a result. Either way, the solution is simple: more water!

5Your Body Feels Heavy And Weak When You Try To Move

Maybe you're going on a jog and you notice that your legs seem a bit harder to move than usual, or perhaps you're just walking up the stairs in your apartment building and it's just a little too difficult for some reason, to the point where you're fully out of breath by the time you reach your front door.

Research from the Journal of Athletic Training shows that feeling fatigue in your muscles is another sign that you might need to hydrate a bit more throughout the day. And, if you find yourself actually cramping during a workout, that could definitely be another sign of dehydration, according to Everyday Health.

6Your Breath Is Low-Key Gross

As Reader's Digest reports, you need saliva in your mouth to wash away the particles of food on your tongue and between your teeth that can cause bacteria to grow. So, if your mouth is dry, well, you do the math. The bacteria can stick around, grow, and cause your breath to be a little less than fresh.